Meet the Grandduggar!

With a scrunch of her tiny button nose, 2-day-old Mackynzie Renée Duggar opens her pink lips and pulls off a seemingly impossible task: She lets out a shriek that drowns out all 17 of her aunts and uncles (plus Grandma and Grandpa Duggar), who have packed into her parents' Fayetteville, Ark., living room to meet their new niece. "It's hard to get louder than that, honey!" says her beaming mother, Anna. New dad Josh scoops her into the crook of his arm and smiles as she grabs his thumb. "Even when she's awake at 3 a.m.," he says, "it's a blessing."

Even for a family that's accustomed to baby arrivals—after all, they star in the TLC reality show 18 Kids and Counting—the newest Duggar is truly one of a kind. Born Oct. 8, Mackynzie Renée (Mackynzie after Josh's cousin, and Renée is Anna's middle name too) is the first grandchild for Jim Bob, 44, and Michelle, 43, who are themselves expecting a new baby in the spring. (In addition to Josh, 21, their children include twins Jana and John-David, 19; Jill, 18; Jessa, 16; Jinger, 15; Joseph, 14; Josiah, 13; Joy-Anna, 11; twins Jedidiah and Jeremiah, 10; Jason, 9; James, 8; Justin, 6; Jackson, 5; Johanna, 4; Jennifer, 2; and Jordyn, 9 months.) "I can't believe I'm old enough to be a grandfather," says Jim Bob, laughing. "All these kids are keeping us young."

And busy. While Mackynzie sleeps and Anna rests, Michelle, Jim Bob and the older kids wash dishes, fold laundry and get lunch prepared, and the younger ones play with toys on the floor. "Until I saw everyone here at once, I hadn't really realized how many aunts and uncles Mackynzie has," says Anna, 21. "There's a huge team of people caring for us."

Yet when Anna went into labor on Oct. 8, that team was MIA, participating in a family church camp in Texas. With their doctor also out of town, the couple opted to labor at home for as long as possible with support of a doula (birthing assistant). When they got word of Anna's labor, Michelle and Jill hopped a plane home, arriving just minutes before Mackynzie was caught by Josh, who helped clamp and cut the cord. "It was," he says, "an incredible moment."

And one that he hopes to relive as often as possible. Following in the footsteps of his parents—"We accept the children we have as blessings from God," says Jim Bob—Josh says he and Anna "will welcome as many children as God will give us." Anna agrees: "I can't wait to see what might happen with the next one!"

But for now, it's all about Mackynzie. After a busy day of meeting all her aunts and uncles, she snuggles up with Anna, snoozing while her youngest uncle, Jackson, quietly looks on. Meanwhile, Anna is brushing up on parenting tips from her seasoned mother-in-law. "She's like a living birth encyclopedia," says Anna. Counters Michelle: "Anna's doing so well. She's a wonderful mother." Josh surveys his new family and nods. "Time is really flying by, and kids grow so quickly," he says. "I want to live in the moment and cherish it. Even it if happens at 3 a.m."